(a) Field of the Invention
The present invention relates to a GPRS (general packet radio service) network system and, more particularly, to a GPRS network system which is capable of mobile communication without significantly modifying the structure of the current GPRS network system while adding some interfaces, for example, thereto.
The present invention also relates to a mobile communication method used in such a GPRS network system.
(b) Description of the Related Art
GPRS is known as a packet switching service using a GSM (global system for mobile communication) backbone network. The GSM network system is a digital cellular phone system prescribed in the unified European telecommunication standard.
The techniques for the telecommunication system used in the GPRS network system are described in JP-A-2000-201172 and PCT domestic publication 2001-517910, for example. Other PCT domestic publications 2000-503825, 2001-508970 and 2001-508971 also describe techniques for the GPRS communication networks.
FIG. 8 shows a block diagram of a typical communication system using the conventional GPRS system, wherein a public land mobile network (PLMN) 300 and an IP network 200 are depicted. A plurality of base stations (not shown in the drawing) in the PLMN 300 are connected to one of the higher-order-node radio network controllers (RNC) 55 to 58, and communicate with subordinate mobile stations such as mobile stations 59 and 60, i.e., mobile stations staying within the cellular area of the base station and thus belonging to the base station. Each radio network controller RNC constitutes a starting point and a terminal point of a GTP encapsulating using the GPRS tunneling protocol (GTP).
Principal nodes constituting the GPRS network 300 include two types of node including a support node SGSN (serving GPRS support node) as a lower-order node and a gateway node GGSN (gateway GPRS support node) as a higher-order node. These support node SGSN and gateway node GGSN have a function of relaying communication between a user terminal (or source mobile station) and a destination mobile station.
A support node SGSN 53 or 54 effects data transmission between the same and the mobile station such as 59 or 60 or a gateway node GGSN 52 in the PLMN 300. For example, a support node SGSN 53 collects up-link calls from the subordinate radio network controllers RNC 55 and 56 and distributes the down-link calls delivered from a superordinate gateway node GGSN 52 toward the subordinate radio network controllers RNC 55 and 56. The support node SGSN 53 manages a packet service between the same and the gateway node GGSN 52 by tunneling. The support nodes SGSN receive the subscriber data stored in a home location register (HLR) 51 and have therein at any time a copy thereof.
It should be noted that the public land mobile network (PLMN) 300 is one of communication areas under the control of a mobile communication carrier. It is usual that a large number of support nodes SGSN are provided in a PLMN 300; however, only two of the support nodes SGSN 53 and 54 are depicted in FIG. 8.
The home location register HLR 51 is a database node for storing subscriber data including registered location information of the mobile stations and accounting information thereof, and delivers a copy of the subscriber data to the support nodes SGSN 53 etc. upon request therefrom. More specifically, the home location register HLR 51 stores permanent subscriber data as to each of the mobile subscribers, such as including a mobile station ISDN number (MSISDN) which specifies a proprietary mobile subscription by using a PSTN numbering plan, and an international mobile subscriber identity (IMSI) which is a proprietary identity or ID allocated to each subscriber and used for identification during the signal transmission in the mobile network system.
The home location register HLR 51 also stores therein data including the current subscriber location number corresponding to the address of VLR (visitor location register) in service for the mobile subscriber and a list of the services allowed to the mobile subscriber. All the information for the subscriber with respect to the network is stored in the HLR 51 in relation to the IMSI of the subscriber. It should be understood that the location registry of each mobile station MS in the home location register HLR 51 is effected via the support node SGSN, the address of which is also stored as the SGSN address in the home location register HLR 51.
The gateway node GGSN 52 functions as a logical interface to an external data packet network such as an IP data network 200, and operates for coupling between networks 300 and 200. More specifically, the gateway node GGSN 52 collects up-link calls from the subordinate support nodes SGSN 53 and 54 and accesses the external IP data network 200. In FIG. 8, it is assumed that the IP network 200 is to be accessed at the gateway node GGSN 61 of the IP network 200 as an access point. The gateway node GGSN 52 in the GPRS network 300 sets up a tunnel down to the support nodes SGSN 53 and 54 for down-link calls.
It is noted that the specification for the current 3GPP (third-generation partnership project) is only directed to traffics wherein a mobile station either originates a call to a server or host computer within the internet or answers a call from the server or the host computer. That is, in the current 3GPP, there is no specification that prescribes the traffics between the mobile stations within the same GPRS network 300.
However, it is considered that a demand for communication occurs between mobile stations both residing within the same radio communication network, and in an extreme case, a demand for communication may occur between mobile stations staying within the same area of the radio communication network, such as within the same building.
Thus, as the present inventor considers, it is preferable that such a communication be performed within the same GPRS network. Particularly, considering that a mobile-to-mobile communication can be achieved by setting a return path at a node within the network, such a return path is especially preferable because reduction of the communication path or avoidance of congestion at the gateway node GGSN is obtained. For this purpose, it is desirable to add some architecture in the scheme of the 3GPP system of the GPRS configuration. This should be achieved as by adding a new-type node in the network without introducing a significant modification of the structure in the system, which raises the development costs or implementation costs.